This deck can win in several ways. It of course can go for commander damage, as a 6/6 with deathtouch for five is nothing to sneeze at, but that is less effective in multiplayer games. My preferred method to win in this deck is with a combo. Ob Nixilis, the Fallen into a large Scapeshift, almost always kills one or more players, particularly if you follow it up with a Splendid Reclamation. It also makes Ob Nixilis huge, so he can be sacrificed to Jarad, Golgari Lich Lord to kill everyone else, or just attack. Another option is to use Dakmor Salvage, Wild Mongrel, and Jarad while Gitrog is in play to make the mongrel infinitely large and pitch it to Jarad. Wild mongrel can be replaced with Oblivion Crown and any other creature, including Gitrog itself.
Assume with The Gitrog Monster unless otherwise mentioned
Alhammarret's Archive – What if we could draw thirty instead of fifteen. Also, cycling lands become insane with Girtrog and the archive in play.

Amulet of Vigor + Scapeshift or Splendid Reclamation – Sure, I will basically not spend mana to refill my mana pool. Also an interesting interaction with Mesmeric Orb.

Crucible of Worlds – I think this is self-evident. We are sacrificing our lands a lot. Let’s make that an easier pill to swallow.

Dakmor Salvage – A land with dredge, in a deck that cares about lands hitting the yard. Seems good. This is probably the most important land in the deck. My game plan gets a lot harder when I lose it to exile.

Mesmeric Orb – This is how you draw fifteen cards before your draw step. Because each mill is individual, it does take awhile to resolve, but it is extremely powerful to mill several lands and then draw for each.

Squandered Resources – If you look at the TCGPlayer page for this card, you can pinpoint the exact time The Gitrog Monster was spoiled, based only on the price history graph. It is truly insane in this deck.